3815 90 10: Diğer reaksiyon başlatıcı ve katalizörler: Metanol içinde çözelti halinde etiltrifenilfosfonyum asetat içeren katalizörler

These subheadings cover mixtures based on compounds, the nature and proportions of which vary according to the chemical reaction to be catalysed. They are frequently used in the manufacture of plastics, often under the name of initiators, transfer agents, terminators or telomers, and reticulating (or cross-linking) agents.

They include the following:

1. ‘radical’ catalysts

These are preparations, based on organic substances, which decompose slowly under reaction conditions and produce fragments that, by colliding with the initial monomers, favour the establishment of a bond and the formation of new free radicals capable of repeating the process and propagating the chain.

Amongst these are:

(a) preparations based on organic peroxides of the type R–O–O–R′ (organic solutions of peroxides such as acetyl and dibenzoyl peroxides). During the reaction, RO· and R′O· radicals are formed and act as activators;

(b) preparations, based on azo-compounds (such as azobisisobutyronitrile), which decompose in the course of the reactions, releasing nitrogen and forming free radicals;

(c) redox preparations (for example, a mixture of potassium peroxide and dodecylmercaptan), in which the formation of activating radicals is due to a redox reaction;

2. ionic catalysts

These are generally organic solutions of compounds which generate ions capable of attaching themselves to the double bond and reproducing active sites in the resulting product.

They include:

(a) ziegler-type catalysts for the production of polyolefins (for example, a mixture of titanium and triethylaluminium);

(b) ziegler-natta-type catalysts (stereocatalysts, orientating catalysts), such as a mixture of titanium trichloride and trialkylaluminium, for the preparation of isotactic polypropylene and ethylene-olefin block copolymers;

(c) catalysts for the preparation of polyurethanes (for example, a mixture of triethylenediamine and tin compounds);

(d) catalysts for the preparation of amino-plastics (for example, phosphoric acid in an organic solvent);

3. catalysts for polycondensation reactions

These are preparations based on various compounds (for example, a mixture of calcium acetate, antimony trioxide, titanium alcoholates, etc.).